1. Field of the Invention
This invention relates generally to cleaning of sewage treatment tanks, and more particularly to an apparatus for cleaning the weir, baffle, spillway, and effluent trough surfaces of a sedimentation water treatment tank.
2. Brief Description of the Prior Art
In a typical water treatment facility, raw sewage is received from the sewage system and passed through a coarse screen to remove large pieces of matter. The sewage is next directed to one or more primary sedimentation tanks or clarifiers. The sewage remains in primary sedimentation for a period of time sufficient to allow the majority of the heavy matter to settle to the bottom of the tank, forming sludge. The sludge is removed for digestion by micro-organisms and can be dried for use as compost or fertilizer. The remaining liquid is treated in a second biological system to remove ammonia. The liquid from this treatment is then aerated and passed into final sedimentation water treatment tanks to remove any remaining solid material.
Water treatment tank configurations vary with each treatment facility application. However, most final sedimentation water treatment tanks are round to eliminate inaccessible corners and provide uniform surfaces which simplifies automatic skimming, churning and/or bottom scraping operations.
In most sedimentation water treatment tanks, sediment containing water enters the central influent of the tank and the lighter clean water is continuously decanted from the heavier sediment containing water. Usually, the clean water is displaced from the tank by the constant flow of sediment containing water into the tank. The displaced clean water is forced to flow under a circular baffle plate which collects floating scum and then over a circular weir supported atop a circular spillway radially spaced a distance from the baffle plate, and ultimately enters a surronding circular clean water flow channel, also referred to as a launder channel or effluent trough which directs the water to the next treatment stage where it is further made safe to be discharged into a river or stream. Typically, the circular weir has a V-notched upper portion. An elongate skimmer arm having a depending skimmer blade revolves around the central influent portion of the tank to provide churning and prevent sludge buildup to a limited extent. Many treatment tanks have one or more vertical columns closely adjacent the spillway which support a catwalk extending horizontally over the tank. Also, in many installations the circular baffle plate is connected in spaced relation to the spillway wall by triangular gusset plates.
The exposure of water treatment tanks to direct sunlight promotes the growth of algae. Algae growth is most prevalent on the baffle, weir, spillway, and clean water channel members, and inhibits the flow of clean water from the tank. Further, the algae can be carried in thick masses and high concentrations in the clean water being discharged from the final treatment tank. Thus, the algae removing process must be done frequently, adding to the cost of operation of the facility.
Commonly, cleaning of the treatment tank is accomplished by scrubbing the baffle, weir spillway, and clean water flow channel by hand with brushes to remove the algae. This method is tedious, labor intensive, and costly.
There are several patents which disclose various algae removal and cleaning apparatus for use in sewage treatment tanks. However, most of these are relatively complex mechanisms having a system of brushes and supporting arms which are designed to simultaneously clean the inside and outside surfaces of the baffle, the inside surface of the weir, and the opposed side surfaces of the clean water flow channel.
Because most treatment tanks are quite large, usually 60 feet in diameter or more, the baffle plate, weir, spillway, and clean water flow channel or launder channel are not perfectly circular. Thus, in a single tank, there are wide variations in the radial distance from the center of the tank to the surface to be cleaned, and variations in the radial distance between the baffle plate, weir, and clean water flow channel relative to one another.
Tank cleaning devices which are connected at the outer end of the rotating skimmer arm and have a system of brushes supported on arms for simultaneously cleaning opposing surfaces of the radially spaced baffle, weir, and clean water flow channel, are difficult to adjust to maintain in constant engagement with the surfaces due to the variations in radial distance and relative spacing of these members, thus in some cases, a brush may not even be in contact with the surface along portions of its circumference, and along other portions, it may engage too tightly and cause binding.
Most prior art cleaning devices of this type are not capable of use in treatment tanks that have one or more vertical columns closely adjacent the spillway which support a catwalk extending horizontally over the tank. Also, many are incapable of cleaning the opposed surfaces and the space between the weir and baffle plate in installations where the circular baffle plate is connected in spaced relation to the spillway wall by triangular gusset plates, or else require replacement of the existng gussets with different support means.
Another disadvantage of these types of devices is that they only clean one side of the weir, not both sides, and thus, do not effectively remove algae from both sides, nor effectively prevent buildup of algae and foreign matter in the notches of weirs having notches.
Riddle, U.S. Pat. No. 4,876,010 discloses an apparatus which is connected to a revolving arm for cleaning a sewage treatment tank. The apparatus has a series of nozzles, a skimmer blade, a first brush supported on a first arm for cleaning the exterior surface of a circular barrier and a pair of articulated arms which are positioned on each side of a hexagonal effluent channel which is U-shaped in cross section with the upstanding portions defining an inner and outer weir A brush is connected to each articulated arm for cleaning only the exterior surface of the inner weir and only the exterior surface of the outer weir, respectively.
Hall, U.S. Pat. No. 4,830,748 discloses an apparatus which is connected to a revolving skimmer blade for cleaning algae and other debris from a round water treatment tank. The apparatus has a first set of three cleaning brushes which clean the inside and outside surfaces of the baffle and the inside surface of the weir. The brush for cleaning the inside surface of the baffle is mounted on its own support arm. A coil spring is provided between the support arm and main frame member to urge the cleaning brush into positive engagement with the inside surface of the baffle wall. The brushes for cleaning the outside surface of the baffle and the inside surface of the weir are mounted on a second support arm and face outwardly in opposite directions. These brushes are pivotally mounted on the base of the second support arm and are urged by a spring into substantially vertical alignment when placed in the operative cleaning position.
Hall, U.S. Pat. No. 4,978,447 discloses a self-propelled motorized carriage apparatus for cleaning algae and other debris from a round water treatment tank. The carriage apparatus has four wheels, two of which ride on the spillway, and the other two are supported in a C-shaped guide track channel installed on the inner wall of the clean water flow channel. Alternatively, the guide track channel can be eliminated by providing carriage apparatus with two wheels which ride on the spillway, and two wheels which are supported on the top surface of the spillway, and pinch rollers which are engaged on both sides of the weir and/or baffle. The apparatus has a first set of three cleaning brushes which clean the inside and outside surfaces of the baffle and the inside surface of the weir, a second set of brushes for cleaning the spillway, and a third set of brushes for cleaning the bottom and opposed side surfaces of the clean water flow channel.
The present invention is distinguished over the prior art in general, and these patents in particular by an apparatus for cleaning algae and debris from the weir, baffle, spillway, and effluent trough surfaces of a sedimentation water treatment tank. A main frame is mounted on the revolving skimmer arm of the tank. A pair of weir cleaning brushes mounted at a lower end of an articulated link arm assembly have bristles facing in inwardly opposed relation engage and clean both sides of the weir and move inward and outward relative to the center of rotation to compensate for out-of-round circular weir surfaces and pivot when their lower ends engage a bracket or obstruction so that they pass thereover and return to a vertical position. A sweeper connected with the weir cleaning brushes spans the space between the baffle and the weir and has elongate flexible strips that dislodge algae and debris and facilitate is passage through the weir and may also clean the surfaces of the baffle and weir. A vertical spillway cleaning brush and a vertical peripheral wall cleaning brush connected at the lower ends of respective support arms engage and clean the outer surface of the spillway and the inner surface of the peripheral wall and move in a horizontal inward and outward direction relative to the center of rotation of the skimmer arm to compensate for out-of-round and imperfect circular wall surfaces and pivot about a vertical axis should they contact an obstruction and then return the engaged position after passing over the obstruction.